Induction motors are conventionally used in controlling the operation of a pipeline pumping station. Due to the nature of pipeline operations, these motors are intermittently operated to turn the pumps ON and OFF. The starting current required for operating large induction motors is sufficient to cause a heat build-up in the windings. Too great a heat build-up can damage the windings. It is therefore important that the motor be run long enough to dissipate this start-up heat or, in the alternative, turned OFF long enough to dissipate the heat prior to a subsequent starting of the motor.
Various system malfunctions can cause the pumping operation to be started too frequently for safe operation of these large induction starting motors. Two such examples are resistor failures in the unit starter, resulting in a pulsing of the starter, and pressure fluctuations at pressure controlled stations. Various electromechanical devices have been utilized to prevent these malfunctions from resulting in heat build-up damage to the starting motor. Such devices have included stepping switches and timers for counting the number of motor startings and ensuring a minimum cooling time between each starting.